In both residential and commercial roofing applications, a primary roof covering material provides the main water protection barrier. Whether the primary covering is composition shingles, metal panels or shingles, concrete or clay tiles, wood shakes, or slate, it is the function of the primary roofing material to protect the building interior from water ingress.
In some circumstances, whether due to primary roofing material design, installation practices, or accidental breach of the primary roofing material, water can penetrate the primary roofing material. To protect the building interior in these circumstances, it is common to use a secondary water shedding device called a roofing underlayment which acts as a temporary water shedding device.
A variety of roofing underlayment products are commonly used. The two major classes are mechanically attached and self-adhered underlayments, the latter commonly referred to as “peel and stick”.
It is desirable that a roofing underlayment provide a surface which has a sufficiently high coefficient of friction (“COF”) to be safe for an applicator to walk upon. The phrase “high coefficient of friction” in this document means a static coefficient of friction of at least 0.8 or a dynamic coefficient of friction of at least 0.8. Underlayments should be easily affixable to a roofing surface, for example by nailing or adhesion. They should ideally be impermeable to moisture. High tensile and tear strengths are also desirable to reduce tearing during application and exposure to high winds. Underlayments should be light in weight to facilitate ease of transport and application, and should be able to withstand prolonged exposure to sunlight, air and water.
A common mechanically attached roofing underlayment product used in the United States and Europe is bituminous asphalt-based felt, commonly referred to as felt. Typically, this felt comprises organic paper felt saturated with asphaltic resins to produce a continuous sheeting material which is processed into short rolls for application.
Such felts generally demonstrate good resistance to water ingress and good walkability in dry and wet roof conditions. Disadvantages include very low tensile and tear strengths, relatively high weight per unit surface area, a propensity to dry and crack over time, extreme lack of resistance to ultraviolet (“UV”) exposure, high likelihood of wind blow off, and a propensity to absorb water causing buckling and wrinkling, thus preventing the application of direct primary roofing materials such as composition shingles.
As felts have very low tensile and tear strengths, their use is generally confined to roofing applications where the roofing underlayment is attached directly to a solid, continuous roofing deck, rather than in spaced sheathing applications where open spaces characterize the roof structure. Use of felts in spaced sheathing roofs would endanger the applicator should the applicator walk over a section of the roof structure covered only by felt.
In climatic regions where ice damming or prolonged exposure to water is prevalent, it is common to employ thick rubberized asphalt-based underlayments in the valleys, eaves, and seams of the roof. These underlayments are generally applied not by mechanical means, but by adhesives exposed by removing release liners from the bottom surface of the underlayment.
In Europe, it is common in roofing design to utilize spaced sheathing rather than solid decking prior to application of the primary roof covering materials. To address the safety issue of an applicator falling through rafters, several products have been marketed with high tensile and tear strengths which are specifically designed to prevent applicator breach during application.
These materials are generally reinforced membranes such as woven hybrids with other laminates or coatings, or reinforced non-woven polymeric synthetic materials, rather than asphaltic felts. They are generally lightweight, thin, have high tensile, tear and burst strengths, and are superior to felts in UV resistance and resistance to drying and cracking over time.
The major drawback of such underlayments is their low COF on the walking surface in dry or wet conditions. This problem limits the commercial attractiveness of such products in high pitch roofs or in climates characterized by frequent and sporadic wet or humid conditions. It has limited these products to spaced sheathing applications where safety and tensile strength are more important than walkability.
In many markets, such as the US and Canada, building design is characterized by roofing structures possessing solid decking substrates onto which is applied roofing underlayment and, ultimately, the primary roofing material. As the decking surface provides a safe walking medium for the roof applicator, underlayment walkability, that is, the ability to permit applicators to walk upon the underlayment without slipping, becomes more important than tensile strength. Any roofing underlayment which does not provide walking safety under dry and wet conditions will be unsafe for use without special precautions, and will be severely limited in commercial market penetration.
Such underlayments include RoofGuard™ and RoofTOPGuard II™ produced by Rosenlew of Finland. These are produced using woven tape technology as a reinforcement, and are two-sided polymer-coated for encapsulating the porous woven substructure. RoofGuard™ utilizes smooth, high COF polymers to improve walkability in dry conditions. However, it suffers dramatic reduction in COF in wet conditions.
In RoofTOPGuard II™, the walking surface has been replaced by a polypropylene spun bond non-woven layer. This surface provides a slight improvement in walkability in some wet surface conditions. However, it does not provide safety in highly pitched roofs and very wet conditions. The non-woven material also has a tendency to peal or suffer surface fiber tears under foot load, and does not readily absorb or displace water when walked upon. Therefore, this product is limited in its ability to compete with felt roofing underlayments under wet conditions.
TRIFLEX 30™, produced by Flexia Corporation of Canada is of spun bond polypropylene construction, with a polypropylene layer coating both sides. The surface is relatively smooth and void of any surface texture properties which would provide high COF properties under wet or dusty conditions.
There are other examples of underlayment products, notably in the self-adhered or “peel and stick” bituminous membrane market, which possess various surface designs aimed at improving walkability under wet conditions. Grace Construction Products produces various rubberized asphalt self-adhered products, including Select™ and Ultra™, having either a grainy polymer film laminate surface or an embossed polymer adhesive pattern as a surface layer. Neither product, however, works well under wet or dusty conditions.
Polyglass produces Polystick P™ and Polystick MU™ self-adhered underlayment with polymer corrugated film laminated and non-woven fabric surfaces. Neither of these products works very well in wet conditions, as there is no mechanism to generate high normal and shear forces under walking load to resist slippage.
Additional mechanical and self-adhering membrane roofing underlayment products are shown in Table 1, in which “M” refers to mechanically applied underlayments and “SA” to self-adhered underlayments. All of the abovementioned materials, as well as all materials in Table 1, were tested in simulated test roof pitches ranging from a 4:12 pitch (a vertical rise of 4 units over a horizontal distance of 12 units) to a 12:12 pitch under extremely wet surface conditions. All materials were found to possess surfaces that become highly slippery and unsafe to walk upon when coated with water.
TABLE 1Roofing underlayment productsSupplierTypeTrade NameSurface Layer TypeMFM BuildingSAIce Buster ™silver, embossed polymer filmProductsMFM BuildingSAWind & Waterblack, grainy polymer filmProductsSeal ™TAMKOSATW Tile andblistered surfaced filmMetal ™MiradriSAWIP 200 ™black, embossed polymer filmLafargeMDivoroll Top ™black, non woven fibersDupontMTyvek Solid ™white, tan, pitted spun bondedDaltexMRoofShield ™grey, embossed non wovenfibers
Wiercinski, in U.S. Pat. No. 5,687,517, describes a roofing underlayment with corrugated ridges in the machine direction to achieve slip resistance in installation on a sloped roof. The surface layer comprises oriented, corrugated film laminated onto substrate. These ridges comprise polymer materials having a low COF under dry or wet conditions. These ridges do not provide sufficient shear and normal force resistance under loading, as the individual ridges lack rigidity and bend over. Such an underlayment does not function well under wet conditions.
Strait, in U.S. Pat. No. 6,308,482, describes a reinforced roofing underlayment with a tensile strength sufficient to resist tearing when exposed to tensile loads from various directions. He further discloses provision of a slip-resistant polypropylene sheet on the outer surface of the roofing underlayment.
Neither of the above patents discloses satisfactory slip resistance under wet, humid or dusty conditions at high roof pitches between 4:12 and 12:12. Neither discloses an invention in which the bottom layer is resistant to slippage between the underlayment and the deck during installation, nor do they combine high tensile strength and slip resistance on both sides of the underlayment.
One method in the prior art of achieving a high COF under wet conditions is by embedding extremely hard, granular, inorganic particles into the surface of asphalt bituminous underlayments.
Polymer underlayments are produced by various forms of polymeric extrusion, lamination, or thermal calendaring. In extrusion coating methods, it is normal to use specially surfaced chilling rolls to quench the molten polymer to solidify the product and reduce thermal damage of the reinforcement. The use of hard inorganic particles would severely damage processing equipment, and also significantly increase the mass per unit area of the resulting underlayment, limiting the advantages inherent in lightweight synthetic polymer underlayments.
Adding hard particles to the throat of an extruder to produce granular coatings would not be feasible as it would damage the processing equipment. Particles would be unable to pass through normal filtration media or narrow die slits. Furthermore, adhesion between inorganic particles and thin thermoplastic coatings is generally very poor, permitting the particles to dislodge from the underlayment surface.
The use of specialty inorganic particle coatings could improve bonding to the underlayment surface, but would add technical complexity and cost. Also, hard inorganic particles may tear and gouge the relatively soft surface layers of the polymer underlayment if freed from the surface and walked upon, thereby permitting water penetration of the underlayment.